Gas turbine engines are typically employed to power aircraft. Typically a gas turbine engine will comprise an axial fan driven by an engine core. The engine core is generally made up of one or more turbines which drive respective compressors via coaxial shafts. The fan is usually driven directly off an additional lower pressure turbine in the engine core.
The fan comprises an array of radially extending fan blades mounted on a rotor and will usually provide, in current high bypass gas turbine engines, around seventy-five percent of the overall thrust generated by the gas turbine engine. The remaining portion of air from the fan is ingested by the engine core and is further compressed, combusted, accelerated and exhausted through a nozzle. The engine core exhaust mixes with the remaining portion of relatively high-volume, low-velocity air bypassing the engine core.
The fan blades may be manufactured from metallic or composite non-metallic materials. Generally composite non-metallic fan blades include a body formed from fibres within a resin matrix.
During operation of the gas turbine engine, the fan blades may be impacted by a foreign object (such as a bird) or if a failure occurs the fan blade may be impacted by another fan blade that has been released from the remainder of the fan. In such impact events the integrity of the fan blade should be maintained. A failure mechanism of concern for composite fan blades is delamination.
To resist delamination the fan blade may be reinforced, for example using through thickness reinforcement rods, known in the art as z-pins. U.S. Pat. No. 7,008,689 is an example of a fan blade that is reinforced using z-pins. U.S. Pat. No. 7,008,689 is concerned with providing a different number of z-pins depending on the strain energy of the blade created in a particular region during loading of the blade. In this way the strain energy of the blade is substantially uniform across the blade so as to have consistent resistance to delamination across the blade.
Although reinforcing the fan blade using z-pinning has been found to be effective for resisting delamination, reinforcement undesirably increases the cost of the fan blade.